Abstract
Heritable changes of phenotype arising in plant ontogenesis by the influence of environmental factors belong to the most intriguing genetic phenomena. An unusual inheritance pattern was detected during examination of male fertility restoration in the CMS-inducing “9E” type cytoplasm of sorghum: Rf-genes were functional in self-pollinated progeny of F1 hybrids yet were either not expressed or poorly expressed in backcrosses of these hybrids to CMS-lines with the same cytoplasm type. In experiments on parallel growing of the same F1 hybrid combinations in the “dry plot” and in the “irrigated plot,” it was found that high level of plant water availability during panicle and pollen developmental stages significantly increased male fertility of F1 and test-cross hybrid populations, in which fertility-restoring genes were in heterozygote state, whereas in F2 populations the influences of water availability conditions cause less pronounce effects. Similarly, male-sterile F1 plants, being transferred from the “dry plot” to greenhouse, produced male-fertile panicles. In addition, male-sterile plants from F2 families, which segregated-out as recessives, being transferred to greenhouse also produced male-fertile panicles. In the progenies of these revertants that were grown in field conditions and in the “dry plot,” stable inheritance of male fertility for three cycles of self-pollination was observed, and a number of stable fertile lines in the “9E” cytoplasm were obtained. However, in test-crosses of these fertile lines to CMS-lines with the “9E” cytoplasm restoration of male fertility was not observed, except the progeny of one revertant that behaved as fertility-restorer line. These data suggest that the functional state of fertility-restoring genes for the “9E” sorghum cytoplasm is epigenetically regulated trait established by the influence of environmental factors and is transmitted to sexual generations.
Highlights
Interaction of plant genotype with environment is one of the central problems of plant genetics
Nuclear and cytoplasmic genes involved in genetic control of cytoplasmic male sterility (CMS) – maternally heritable failure to develop fertile pollen – belong to genetic systems, which are strongly sensitive to environmental factors
In the majority of the combinations analyzed sterile plants appeared in the F1 and BC1 generations in the “dry plot” ([9E] Rannee-7/KVV263; [9E] Milo-10/Pers-1; [9E] P-614/Pers-1), whereas only fertile ([9E] Milo-10/Pers-1) or fertile and ps-plants were observed in the “irrigated plot” ([9E] Rannee-7/KVV-263; [9E] P-614/Pers-1)
Summary
Interaction of plant genotype with environment is one of the central problems of plant genetics. Environmental factors, such as, temperature, water availability, lighting conditions, mineral nutrition regulate expression of plant genes affecting diverse epigenetic processes – DNA methylation, histone modification, micro-RNA formation (Grant-Downton and Dickinson, 2005; Pfluger and Wagner, 2007; Phillips et al, 2007; King et al, 2010; Fisher and Franklin, 2011; Wang et al, 2011). It is generally accepted that CMS is caused be expression of specific mitochondrial genes originating from high recombination activity peculiar to mitochondrial genome (Chase and Gabay-Laughnan, 2004; Hanson and Bentolila, 2004; Fujii and Toriyama, 2008) These genes encode proteins impairing mitochondrial functions at the stage of microsporogenesis and/or microgametogenesis. Such fertility-restoring genes usually have dominant mode of expression
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